DESCRIPTION: (Applicant' Description) The long-term goal of this project is to elucidate how host-tumor interaction regulates in vivo gene expression and physiological function. This project will focus on (a) the mechanisms of upregulation of VEGF and bFGF, two of the most potent and clinically relevant angiogenic molecules, and (b) their putative roles in tumor angiogenesis, vascular permeability, and leukocyte-adhesion. To accomplish this, we will express the green fluorescent protein (GFP), an in vivo reporter, driven by the VEGF/bFGF promoter in mice and different tumor cell lines. By transplanting these cells in different host organs, we will test the hypothesis that the host-tumor interaction influences VEGF/bFGF promoter activity in stromal as well as tumor cells (Aim 1). We will determine the type of host cells that contribute to VEGF/bFGF promoter activity by in vivo confocal laser microscopy, immunohistochemistry and electron microscopy. Using optical imaging techniques recently developed in our laboratory to measure pH, pO2 and GFP in vivo, we will test the hypothesis that VEGF promoter activity is upregulated by both hypoxia and low pH (Aim 2). Finally, by deleting and/or overexpressing VEGF/bFGF genes, and then growing these tumors in different sites in mice, we will determine how the host organ influences the relationship between gene expression and physiological function (Aim 3). Tumor types to be used include glioblastoma, melanoma, and colorectal carcinomas. The sites will include the brain, skin and liver, which are either orthotopic or ectopic for these tumors. Physiological parameters will include vessel density, diameter and tortuosity as measures of angiogenesis, and blood flow rate, vascular permeability and leukocyte-adhesion as measures of microvascular function. Most preclinical studies are currently carried out by growing tumors subcutaneously (ectopic site for most tumors), but the results often fail to predict the response of orthotopically growing primary and metastatic tumors to the same treatment. Therefore, the insight gained in this project will have significant implications for improving current pre-clinical and clinical treatment protocols. It will also suggest novel targets (stromal cells) and strategies (modulation of gene expression) to overcome some of the physiological barriers to the delivery of therapeutic agents to solid tumors, and introduce a new paradigm to study the dynamics of gene expression and function in vivo.